The present invention relates to an ion drive for a spacecraft, comprising a high-frequency generator for generating an alternating electromagnetic field for the ionization of a propellant and a suitable system for ion acceleration.
In space flight, electrical engines are being used to an increasing extent to propel satellites or space probes after their separation from a boost vehicle. Electrical engines are used especially for a trajectory correction of geostationary communication satellites (so-called station-keeping). Above all, ion engines and SPT plasma engines are used for this purpose. Both of these types of engines generate their thrust by emitting accelerated ions. In order to avoid a charging of the satellite, the emitted ion beam is neutralized. The electrons usually required for this are provided from a separate electron source and introduced into the ion beam by means of plasma coupling.
In high-frequency ion engines (Radio Frequency Ion Thruster, RIT), the propellant is ionized with the aid of an alternating electromagnetic field and then accelerated in an electrostatic field to generate thrust. After the passage of a neutralizer, which feeds electrons to the ion beam again and balances the generated positive space charge, the particles are emitted in the form of a beam. To operate this ion drive, a gas supply, an HF generator for generating the alternating electromagnetic field and high-voltage sources for generating a field accelerating the charge carrier are necessary. With conventional grid systems for generating the electrostatic field for ion acceleration, the voltages of the high-voltage generator and of the grid system must be coordinated to generate thrust. Likewise, at least one voltage source is required for the neutralizer for neutralizing the positive ion beam by electrons from an electron source.
The ion drive is characterized by a simple structure and high reliability. However, a high degree of complexity results due to the electronic assemblies required for the voltage supply of the components described.
It is therefore an object of the present invention to provide an ion drive for a spacecraft, in particular an RIT engine, which is structurally simpler in design and can be produced more cost-effectively. Another object of the present invention is to provide a method for operating an ion drive, in particular an RIT engine, in which the operational reliability can be increased and the control effort can be minimized.
These and other objects are attained by an ion drive with the features of claim 1 and by a method with the features of claim 15. Advantageous embodiments are shown by the dependent claims.
The present invention creates an ion drive for a spacecraft, comprising a high-frequency generator for generating an alternating electromagnetic field for the ionization of a propellant, in particular a gas, and a system for accelerating the generated charge carriers. The invention is characterized in that the ion drive comprises a first means with which the high voltages that are necessary for the system to accelerate the generated charge carriers from the currents and/or voltages generated by the high-frequency generator to generate the alternating electromagnetic field can be derived.
The ion drive according to the invention is a high-frequency ion drive, in particular a radio-frequency ion thruster (RIT). A gas, such as xenon, can be used as a propellant. The ion drive according to the invention has the advantage that the mass of the ion drive can be reduced compared to conventional ion drives due to the simplification of the voltage supply system. At the same time, operational reliability can be increased and control effort can be minimized.
In one embodiment, the first means is embodied to draw at least the high voltage(s) necessary for ion acceleration from the currents and/or voltages generated by the high-frequency generator for generating the alternating electromagnetic field. With a conventional two grid acceleration system, the first grid is a screen grid and the second grid is an acceleration grid. If the grid system comprises more than these two grids, the high voltages required for the further grids are also derived by the first means from the currents and/or voltages generated by the high-frequency generator.
In a first embodiment, the first means has at least one capacitor coupled to the high-frequency generator for coupling out a part of the power generated by the high-frequency generator.
In an alternative embodiment, the first means for coupling out a part of the power generated by the high-frequency generator comprises at least one coupling coil coupled to the high-frequency generator, at the coil terminals of which coupling coil the voltages necessary for the grid system are provided. In particular, the at least one coupling coil is embodied in the form of a secondary winding of a transformer, which is coupled to a coil of the high-frequency generator as primary winding of the transformer. The high-voltage transformer, which can be integrated into the high-frequency system, provides at the output thereof the voltages for the acceleration system. It can furthermore be provided that the at least one coupling coil has respectively one or more taps, wherein it is or they are galvanically separated from a coil of the high-frequency generator.
Optionally, a second means can be provided for rectifying the voltages derived from the high-frequency generator for the grid system. In particular, a rectification of the voltages for the acceleration system of the ion drive, the ion sources, the neutralizers or the electron sources is provided.
Furthermore, it can be expedient to provide a third means for smoothing the rectified voltages for the acceleration system. The smoothing can be formed by a network of coils (L) and/or capacitors (C) and/or impedances (R). In particular, an LC, an L, a C or an RLC network can be provided for smoothing. The network of coils and/or capacitors and/or impedances is furthermore used to optimize the phase position at the acceleration system. For a radio frequency ion thruster, phase position and voltages on the acceleration system may be adjusted such that the average ion beam corresponds to an average electron beam. As explained above, the latter can also be provided by a separate neutralizer.
For proper operation of the ion drive, the respective components must be operated with a corresponding voltage. The establishment of the voltage ratio between respective voltages of the grid system and the voltages of the high-frequency generator is carried out according to one embodiment by a high-voltage cascade, comprising a number of capacitors and diodes, and/or by the winding ratio of the coil of the high-frequency generator to the coupling coil or coils. Due to a high-voltage cascade, the voltage provided by the high-frequency generator can be increased. A cascading connection of this type is also known under the term charge pump.
According to a further advantageous embodiment, at least one controllable switch is provided between the high-frequency generator and the acceleration system for the time control of the charge-carrier current. The at least one controllable switch can be embodied as a mechanical or electronic switch. In particular, semiconductor switches can be provided.
In a further embodiment, a fourth means for reversing the polarity of the voltages at the grid system is provided for the extraction and acceleration of ions and electrons. In this embodiment, the rectification arranged downstream of the first means can be omitted, since the polarity at the components of the acceleration system with respect to one another changes and alternately electrons and ions are produced. The voltages at the acceleration system may be expediently chosen such that the ion current is equivalent to the electron current. The phase position at the components of the acceleration system can be influenced by suitable RCL networks, as has been explained. A further advantage of this embodiment is that a separate neutralizer can be omitted, which results in a further simplification of the ion drive.
In an alternative embodiment, the ion drive has a neutralizer, wherein a voltage necessary for the operation thereof is derived from the currents and/or voltages generated by the high-frequency generator to generate the alternating electromagnetic field, and is provided in particular by the first means. In this embodiment, the ion drive according to the invention makes it possible to omit a separate voltage source for the operation of the neutralizer. This results in the already explained simpler structural design with reduced mass of the ion engine.
The invention also includes a method for operating an ion drive for a spacecraft, which comprises a high-frequency generator for generating an alternating electromagnetic field for the ionization of a propellant and an acceleration system for generating an electrostatic field for ion acceleration. According to the invention, the high voltages required for the acceleration system are derived from the currents and/or voltages generated by the high-frequency generator for generating the alternating electromagnetic field. The same advantages are associated with this as were explained above in connection with the ion drive according to the invention.
The invention is explained in more detail below based on an exemplary embodiment.